1. (Field of the Invention)
The present invention generally relates to a sealing device in a wheel bearing for an automobile or the like and, more particularly, to the sealing device of a kind integrated together with an encoder grid.
2. (Description of the Prior Art)
The wheel bearing including, as shown in FIG. 37, a sealing device 105 interposed between an inner member 101 and an outer member 102 rotatable to each other through a circular row of rolling elements 103 has been well known in the art. The sealing device 105 shown therein includes an encoder grid 106 integrated together therewith. In this connection, see the Japanese Laid-open Patent Publication No. 6-281018. The prior art sealing device 105 includes generally L-sectioned first and second annular sealing plates 107 and 108 fitted respectively to the inner and outer members 101 and 102 with an elastically deformable sealing lip member 109 secured to the second annular sealing plate 108 so as to intervene between the first and second annular sealing plates 107 and 108. The first annular sealing plate 107 is generally referred to as a slinger. The encoder grid 106 is made of an elastic material mixed with a powder of magnetic particles and is bonded by vulcanization to the first annular sealing plate 107. This encoder grid 106 is of an annular configuration having a plurality of pairs of magnetically opposite poles alternating over the circumference thereof and is cooperable with a magnetic sensor 110 disposed externally in face-to-face relation with the encoder grid 106 for detection of the encoder grid 106.
The first annular sealing plate 107 serving as the slinger and the inner member 101 serving as a rotatable member are engaged with each other under interference fit at an engagement interface 111. However, it has been found that a small quantity of water often ingresses externally into the wheel bearing through the engagement interface 111. Once water ingresses, the first and second annular sealing plates 107 and 108 gather rust, resulting a premature wear of the sealing lip member 109. Also, the grease is prematurely degraded to such an extent as to result in reduction of the lifetime of the wheel bearing.
In view of the foregoing, it has been suggested to reconfigure the encoder grid 106 so that a portion of the elastic material forming the encoder grid 106 extends to an inner peripheral surface of the first annular sealing plate 107 to thereby increase the sealability at the engagement interface 111. However, since the elastic material forming the encoder grid 106 is mixed with the powder of magnetic particles, not only becomes the encoder grid 106 expensive to manufacture, but a required sealing performance is difficult to attain. Also, formation of a relatively thick rubber layer at the engagement interface 111 between the first annular sealing plate 107 and the inner member 101 results in an insufficient engagement therebetween with the consequence that there is a high risk of the first annular sealing plate 107 being separated from the wheel bearing and/or displaced internally of the wheel bearing.
Although instead of the intervention of the elastic material the first annular sealing plate 107 may be made of a soft material to thereby increase the adherence, such soft material is normally of a non-magnetic nature and, therefore, the first annular sealing plate 107 made of such material will fail to provide a magnetic core for the encoder grid 106, resulting in an insufficient density of magnetic fluxes.
The first annular sealing plate 107 may exhibit a sufficient resistance to rusting if it is made of magnetic stainless steel (for example, SUS 430MA) of a kind having a resistance to rusting comparable to that of SUS 304, rather than a generally utilized magnetic material such as SUS 430 of a kind lacking a sufficient resistance to rusting. The magnetic stainless steel referred to above may be SUS 430MA consisting of a stainless steel such as SUS 430 mixed with niobium, Ni or the like to increase the resistance to rusting. As regards the magnetic flux density, SUS 430MA is comparable to SUS 430. However, not only is the magnetic stainless steel referred to above expensive, but even though such material is employed for the first annular sealing plate 107, ingress of water cannot be sufficiently prevented, and therefore, reduction of the lifetime of the wheel bearing as a result of degradation of the grease in contact with water cannot be avoided sufficiently.
FIG. 38 illustrates another prior art wheel bearing. In this figure, components identical with or similar to those shown in FIG. 37 are shown by like reference numerals used in FIG. 37. The sealing device 105 shown in FIG. 38 is shown as employed in the rolling bearing of a type having an inner race rotatable relative to an outer race. The sealing device 105 includes a slinger 107 press-fitted to an outer peripheral end face of the inner race 101, a core metal 108 press-fitted to an inner peripheral end face of the outer race 102 in face-to-face relation with the slinger 107, a sealing member 109 fitted to the core metal 108 and held in sliding contact with the slinger 107, and a rubber magnet 106 bonded by vulcanization to the slinger 107. The rubber magnet 106 referred to above is a pulse generating ring generally used for speed control of a vehicle such as, for example, an automobile. The slinger 107 is of a structure including an cylindrical body 107a having an outer edge formed integrally with a radial flange 107b that protrudes radially outwardly towards the outer race 102. The core metal 108 is of a structure including a cylindrical body 108a press-fitted to the inner peripheral end face of the outer race 102 and formed integrally with an radial flange 108b that protrudes radially inwardly towards the inner race 101 from an inner end thereof adjacent the circular row of the rolling elements 103. An outer end 108aa of the hollow cylindrical body 108a is slightly radially inwardly bent to accommodate the sealing member 109.
The sealing device 105 of the structure shown in FIG. 38 and described above is mounted in position inside the rolling bearing in the manner which will now be described. After the sealing device 105 has been assembled separate and independent of the rolling bearing, the sealing device 105 is press-fitted into the rolling bearing with the slinger 107 mounted on the inner race 101 and the core metal 108 fitted inside the outer race 102. During the press-fitting of the sealing device 105, a plurality of the sealing devices 105 stacked on a support table 114 as shown in FIG. 39 are delivered one by one into a chute by means of a handling unit of an automatic press-fitting machine and is then picked up to be press-fitted in the rolling bearing.
However, since the sealing device 105 shown in FIG. 38 is of a design integrated together with the rubber magnet 106, stacking on the support surface 114 (FIG. 39) the plural sealing devices 105 with the core metal 108 held in contact with the support surface 114 and with the slinger 107, bonded by vulcanization with the corresponding rubber magnet 106, positioned on one side of such core metal 108 remote from the support surface 114 results in contact of the rubber magnet 106 on the slinger 107 in one of the sealing devices 105 with the core metal 108 of the next adjacent sealing device 105 positioned immediately above such one of the sealing devices 105. Considering that the rubber magnet 106 exerts a magnetic force of attraction, the rubber magnet 106 in one of the sealing devices 105 attracts the core metal 108 in the next adjacent sealing device 105 positioned immediately above such one of the sealing devices 105 and, accordingly, a trouble often occurs in delivering the sealing devices 105 one by one by means of the handling unit of the automatic press-fitting machine, thereby hampering a smooth automatic press-fitting.